We have preliminary evidence that small RNAs of the size of siRNA and miRNAs are coupled to modified nucleotides such as coenzyme A and bis-MGD. These modifications would allow small RNAs to covalently engage with the proteome to constitute nucleic acid bar codes on these proteins. We propose to use powerful nucleic acid hybridization and selection techniques to purify the proteins covalently linked to RNA and to use mass spectroscopy to identify those linked proteins. Using RNAi of these proteins we will survey for defects in small RNA function and thus an involvement of these proteins in the functions of small RNAs. Because all of the modifications are predicted to occur at the 5'end of small RNAs, most of these modified RNAs will have been systematically missed by surveys most of which demands 5'OH or 5'phosphates on the RNAs for cloning. PUBLIC HEALTH RELEVANCE: Our preliminary data points to the involvement of modified nucleotides in small RNA function. The implications of this research are enormous: if such small RNAs are the active components of RNAi and miRNA function, as it pertains to the engagement with the proteome, then the field of small RNAs may have systematically missed a major world of small RNAs. In the same way that by not looking at 22 nt for biology, by not being able to detect small RNAs with 5'modifications, the small RNA field may have another dark matter situation. We will remedy this.